Burner system

ABSTRACT

A burner system comprising a source of pressurized air, a source of pressurized gaseous fuel, and a combustion chamber that has an uncooled tubular wall member, and end wall structure secured to the tubular wall member at each end thereof. An inlet port is in one end wall structure and an outlet port is in the other end wall structure. A mixture of air and gaseous fuel is supplied from the sources for flow through the inlet port to the combustion chamber at a steady state velocity in the range of 500-1500 feet per second. Restriction structure spaced from said combustion chamber restricts the flow of transient pressure waves from the combustion chamber towards the sources, increases stability of combustion in the combustion chamber and damps acoustical oscillations in the combustion chamber.

United States Patent [1 1 1 3,926,544 Thorpe Dec. 16, 1975 [54] BURNER SYSTEM [76] Inventor: Merle L. Thorpe, RED. 1,

Concord, NH. 03301 [22] Filed: Dec. 30, 1974 [21] Appl. No.: 537,451

[52] US. Cl. 431/114; 431/158; 431/243; 126/271.2 A [51] Int. Cl. F23R l/02; F23D 11/44 [58] Field of Search 431/158, 114, 207, 215, 431/243; 126/271.2 A

[56] References Cited UNITED STATES PATENTS 2,667,919 2/1954 Pardee et a1 431/243 2,815,019 12/1957 126/2712 2,996,112 8/1961 Arndt 431/243 X 3,258,002 6/1966 Race, Jr. 431/243 X 3,386,475 6/1968 Horton et al. 431/158 3,773,075 11/1973 Thompson et al. 431/114 Primary Examiner-Kenneth W. Sprague [57] ABSTRACT A burner system comprising a source of pressurized air, a source of pressurized gaseous fuel, and a combustion chamber that has an uncooled tubular wall member, and end wall structure secured to the tubular wall member at each end thereof. An inlet port is in one end wall structure and an outlet port is in the other end wall structure. A mixture of air and gaseous fuel is supplied from the sources for flow through the inlet port to the combustion chamber at a steady state velocity in the range of 500-1500 feet per second. Restriction structure spaced from said combustion chamber restricts the flow of transient pressure waves from the combustion chamber towards the sources, increases stability of combustion in the combustion chamber and clamps acoustical oscillations in the combustion chamber.

14 Claims, 3 Drawing Figures BURNER SYSTEM SUMMARY OF INVENTION This invention relates to burners and more particularly to burner systems of the type in which the combustion process occurs in the combustion chamber and a high velocity jet of combustion products is produced, and to burner systems of that type that are particularly useful for removing foreign material from structural surfaces.

It has been difficult to efficiently remove foreign ma terial from structural surfaces. Laborious and time consuming techniques such as sand blasting have been used in the past. Such techniques expose operating personnel to risks such as silicosis, involve problems of cleanup of the abrasive particles used in the same blasting process, are costly and are not particularly efficient. It has been found that a jet of hot gas is useful in cleaning pavement surfaces and an object of this invention is to provide new and improved burner systems that are particularly adapted for removing foreign material from structural surfaces.

The improved burner system in accordance with the invention is useful in the rapid and efficient removal of foreign substances such as paint from structural surfaces such as asphalt and concrete road pavements. The burner system is also useful in cleaning cracks in pavement or similar surfaces prior to further processing such as sealing. In addition to cleaning, the burner action dries the surface thus enabling such operations to be performed during weather conditions that had previously precluded such work.

A burner system in accordance with the invention includes a source of pressurized air and a source of gaseous fuel, a combustion chamber that has an uncooled tubular wall member, and end wall structure secured to the tubular wall member at each end thereof. Inlet port means is provided in one end wall structure and outlet port means in the other end wall structure, the areaof the outlet pofi means being at least 25 percent greater than the area of the inlet port means. Conduit structure supplies a mixture of air and gaseous fuel from the pressurized sources to the combustion chamber, and restriction structure connected to the conduit structure restricts flow of transient pressure waves from the combustion chamber towards the sources. This burner system provides an economical and efficient arrangement which produces a high velocity discharge of combustion products that is particularly useful for removing foreign substances such as painted traffic control lines from structural surfaces. In connec tion with treatment of road pavement surfaces, the high velocity discharge of combustion products acts with volatilizing, flaking and burning action to remove foreign substances without damage to the pavement material. The system makes possible work for longer periods of time throughout the year and also enables working under adverse weather conditions due to the drying effect of the hot stream of combustion products. In like manner the jet of combustion products may be used to remove debris from a pavement crack or groove in a heating and cleaning operation and also to condition the surfaces of the crack or groove for sealing.

During operation, the tubular wall of the simple combustion chamber structure is maintained at an elevated temperature and thus provides a stable high temperature environment in the combustion chamber into which the mixture of air and gaseous fuel is introduced for ignition and flow through. the chamber. The resulting volumetric heat release is much greater than that which could be achieved with a combustion chamber having cooled walls, thus enabling a lightweight, portable combustion system. The length and volume of the combustion chamber is proportioned to the flow rate of the mixture so that combustion is completed within the chamber and the resulting combustion products are discharged in a high velocity jet or swath. During startup, combustion is erratic and explosions and detonations occur, the effect of which on the fuel and air flows from the pressurized sources is moderated by the restriction structure.

In preferred embodiments, the inlet port means is a simple through passage in one end wall and its dimensions are coordinated with the flow rate of the air and gaseous fuel mixture to provide an effective, steady state input velocity in the range of 500-1500 feet per second. As the volume flow of the air-fuel mixture is increased, additional chamber volume together with additional chamber length are employed, for example a doubling of the chamber length accommodates an increase in gas flow of about three times without changing the cross-sectional chamber dimensions. Also in such embodiments the restriction structure included a mixer structure that has an air orifice member in alignment with a converging-diverging nozzle throat structure. The air orifice is disposed in a plenum and the air flow creates a low pressure zone into which the gaseous fuel is introduced. The converging-diverging throat structure provides a change in velocity that mixes the air and gaseous fuel and also a pressure transition which acts as a restriction on the transmission of pressure waves from the combustion chamber rearwardly to the pressurized sources of air and gaseous fuel. Other restriction structures that may be used, either alternately or in conjunction with a mixer, include valves connected to each pressurized source and/or a check valve in the conduit between the sources and the combustion chamber. In embodiments that employ a mixer, the cross-sectional area of the throat is preferably at least 25 percent greater than the cross-sectional area of the air orifice and the cross-sectional area of the combustion chamber port is preferably at least 25% greater than the cross-sectional area. of the throat. The flow conditions in such embodiments enable a stable combustion condition to be established in a simple burner chamber configuration and the efficient production of a continuous, high velocity stream of hot gases that is effective to remove foreign material from structural surfaces.

While a cylindrical chamber is preferred, other tubular configurations may be utilized, including chamber configurations in which the cross-sectional configuration varies along the length of the chamber. The inlet port area in preferred embodiments is less than 15 percent of the average chamber cross-sectional area.

In initiating operation of the system, air and fuel flows are initiated at low flow rates and an igniter mounted on the combustion chamber is energized. An intermittent ignition condition atlow gas flows produces combustion conditions that commence to heat the chamber wall. As the chamber wall increases in temperature, an improved zone for establishing combustion is provided and when "the chamber wall reaches an elevated operating temperature a combustion condition can be maintained without requiring the use of the igniter. Concurrently the gas and air flows are increased to the operating flow rates. The system produces a high velocity jet of combustion products which acts to provide a supporting force for a portable combustion unit so that the combustion unit is essentially floating and maintains itself spaced from the structural surface being cleaned. The resulting jet of combustion products efficiently removes paint and other foreign substances from asphalt and concrete road pavement without damaging the substrate material.

Other objects, features and advantages of the inven tion will be seen as the following description of particular embodiments progresses, in conjunction with the drawings, in which:

FIG. 1 is a view of an apparatus in accordance with the invention;

FIG. 2 is a sectional view through the combustion chamber of apparatus shown in FIG. 1; and

FIG. 3 is a view partially in section of the air-gas mixer assembly of apparatus shown in FIG. 1.

DESCRIPTION OF PARTICULAR EMBODIMENTS The apparatus shown in FIG. 1 includes a portable combustion unit that has a chamber defined by tubular chamber member 12 and end cap members 14, 16. The combustion unit 10 is supported on a rigid conduit 18 to which a handle 20 is secured. A check valve 22 disposed in conduit 18 permits gas flow through conduit 18 to the combustion unit 10 while blocking reverse pressure waves such as produced by flashback and detonation conditions within chamber of the combustion unit 10. A flexible hose 24 extends from conduit 18 to mixer unit 26. Connected to that mixer unit via line 28, and gate valve 30 is a source 32 of air at a nominal pressure of 70 p.s.i.g. Gauge 34, connected to line 36, provides an indication of pressure of air supplied to gate valve 30. Mixer 26 has a second inlet via conduit 38 and needle valve 40 from a pressurized source 42 of propane fuel. Gauge 44, connected to line 46, provides an indication of the pressure of the propane, a nominal value of which is 20 p.s.i.g.

Additional details of the combustion unit may be seen with reference to FIG. 2. That unit has inlet port 50 defined by the end of conduit 52 which is threadedly secured to cap 14. In this embodiment the inner diameter of inlet port 50 (and conduit 52) is 0.62 inch, providing an inlet area of about 0.3 square inches. Threaded bore 54 receives a spark plug 56 which is connected to a suitable ignition power supply (not shown). End cap 14 is welded to the upper end of tubular chamber 12. In this embodiment chamber 58 has a length of inches and a diameter of 2 inches. Lower end cap 16 is similarly welded to the lower end of tubular member 12. That end cap has a nozzle or exit passage 60 which in this embodiment has a diameter of one inch, providing an exit area of about 0.8 square inches. Formed in end plate 16 is an annular chamber 62 which surrounds exit passage 60. Provided in the inner wall of chamber 62 are two annular cooling flanges 64. Couplings 66, 68 are welded to end plate 16 and provide communication through radial ports into the chamber 62. Conduit 18 connected to coupling 68 introduces an air-fuel mixture to chamber 62 and that mixture flows around the nozzle passage 60 to cool the nozzle and also to preheat the combustion mixture while the unit is in operation. The air-fuel mixture then flows through coupling 66, conduit 70, expansion de- 4 vice 72 (FIG. 1), conduit 52 and inlet port 50 into the combustion chamber 58.

Additional details of the mixer structure 26 may be seen with reference to FIG. 3. That mixer structure includes a mixer body member to which is connected lines 28 and 36. Firmly seated against flange 82 by securing ring 84 is air orifice member 86. That member has a flange portion 88, which is seated on an end surface of flange 86, a body portion which is supported by flange 82 and a tubular extension 92. An entrance transition passage 94 of conical configuration is provided adjacent flange 88 and through passage 96 of 0.28 inch diameter extends through the body portion 90 and extension portion 92. Plenum chamber 98 in the mixer body surrounds extension 92 and is in communication with conduit 36 through port 100. Injector throat structure 102 is threadedly connected to the mixer body in coaxial alignment with orifice member 86. That throat member has a convergent entrance passageway section defined by conical surface 104 that has a 7 taper; a cylindrical throat passage section 106 of 0.38 inch diameter; and a divergent exit section 108 that has a taper of 7 /z that is in communication with flexible hose 24 via coupling 110. A A inch gate valve 30 is provided in air line 28 and a V8 inch needle valve 40 is provided in fuel line 38.

To initiate operation, the valves 30 and 40 are cracked open and high pressure air flowing through orifice member 86 entrains fuel from conduit 38 for flow through injector throat 106 in a mixing action and into flexible conduit 24. The combustible mixture flows from conduit 24 past check valve 22 through pipe 18 and into the cooling chamber 62 around the exit passage 60. From that chamber the mixture flows through expansion device 72 and the entrance port 50 into combustion chamber 58. Spark plug 56 is energized to ignite the mixture in combustion chamber 58 at low flow. Combustion of the mixture in chamber 58 commences to heat tube 12 and as the temperature of that tube increases, a zone of elevated temperature is produced in chamber 58. Flow of the fuel mixture is gradually increased with resulting further heating of the chamber tube to an elevated temperature which promotes a stable combustion condition in chamber 58. In stable operation, tube 12 is at a red heat and complete combustion of air-fuel mixture occurs in the combustion chamber. The resulting combustion products pass through the exit or discharge orifice 60 as a high'velocity jet 120 that has a velocity of about 3,000 feet per second and a temperature of about 3,000F. The entering air-fuel mixture is supplied at a rate so that complete combustion occurs as the air-fuel mixture flows through chamber 58. In this embodiment, this stable and complete combustion operating condition is obtainable over a flow range of -200 CFM. Complete combustion is essential to proper operation of the system and too great flow input of the air-fuel mixture will result in incomplete combustion with the walls of the combustion chamber 58 not being sufficiently hot to maintain the stable combustion environment. This stable combustion condition is a function of a relationship between the length of chamber 58, the diameter of the inlet port 50, the-flow rate and the stoichiometry of the gaseous mixture.

While the cross-sectional dimensions of combustion chamber 58 may vary, a chamber diameter of less than 1 inch i.d. would not be considered satisfactory. Further, the length of chamber 58 is preferably at least three times its major cross-sectional dimension.

This burner has been found extremely advantageous and efficient in removing foreign substances from asphalt and concrete road pavement without significant removal of pavement material. It is particularly useful in rapidly, effectively removing traffic control lines from pavement surfaces and also in cleaning random pavement cracks preparatory to repair. The combustion unit in use is manually supported by the operator and the jet 120 of combustion products provides an upward force against that of the force of gravity so that the combustion unit essentially is floating and maintains itself spaced from the pavement surface 122. The operator merely need guide the burner combustion unit to direct the jet 120 to the area where the line of paint 122 to be removed or the crack to be cleaned is located. The jet 120 impinges directly on the material to be removed, and causes rapid volatilization, flanking and/or combustion of the traffic control line material in the path of the jet 120. The velocity of the jet removes debris and the volatilized combusted material from the site and provides a clean pavement surface that needs no after treatment.

In another embodiment, the ejector structure 24 has an air orifice 98 of O. l 6 inch diameter, and a throat 106 of 0.28 inch diameter, and the combustion chamber 58 has a 2-inch diameter and a 7.5-inch length with an entrance port 50 of 0.37 inch diameter and an exit port 60 of 0.5 inch diameter. The system provides a stable and efficient cleaning jet 120 of hot gases at flow rates over the range of about -50 cubic feet per minute.

While particular embodiments of the invention have been shown and described, various modifications thereof will be apparent to those skilled in the art and therefore it is not intended that the invention be limited to disclosed embodiments and departures may be made therefrom within the spirit and scope of the invention as defined in the claims.

What is claimed is:

1. A burner system comprising a source of pressurized air, a source of pressurized gaseous fuel,

a combustion chamber having an uncooled tubular wall member, and end wall structure secured to said tubular wall member at each end thereof, inlet port means in one of said end wall structures, outlet port means in the other end wall structure, the area of said outlet port means being at least percent greater than the area of said inlet port means,

conduit structure for supplying a mixture of air and gaseous fuel from said sources for flow through said inlet port means to said combustion chamber at a steady state velocity in the range of 500-1500 feet per second,

and restriction structure spaced from said combustion chamber and connected to said conduit struc' ture for restricting the flow of transient pressure waves from said combustion chamber towards said sources and damping acoustical oscillations within said combustion chamber.

2. The system as claimed in claim 1 wherein a cooling chamber is formed in said other end wall structure surrounding said outlet port means and said conduit structure is connected to said cooling; chamber, and further including an auxiliary conduit and expansion mechanism connected between said cooling chamber and said inlet port means.

3. The system as claimed in claim 2 and further including an annular cooling flange in said cooling chamber.

4. The system as claimed in claim 1 wherein said restriction structure includes a mixer structure that has an air orifice member disposed in a plenum chamber into which said gaseous fuel is introduced and a converging-diverging throat structure is in alignment with said air orifice member and connected to said conduit structure.

5. The system as claimed in claim 4 wherein the cross-sectional area of said throat is at least 25 percent greater than the crosssectional area of said air orifice.

6. The system as claimed in claim 5 wherein the cross-sectional area of said inlet port means is at least 25% greater than the cross-sectional area of said throat.

7. The system as claimed in claim 1 wherein the length of said tubular wall member is at least three times its major cross-sectional dimension.

8. The system as claimed in claim 7 wherein said tubular wall member is cylindrical in configuration.

9. The system as claimed in claim 1 for use in removing foreign material from structural surfaces wherein said restricting structure includes a mixer unit and said conduit structure includes a rigid conduit member having a handle attached thereto for manipulating the combustion chamber and a flexible conduit member extending between said rigid conduit member and said mixer unit.

10. The system as claimed in claim 9 wherein said mixer unit includes an air orifice member disposed in a plenum chamber into which said. gaseous fuel is introduced and a converging-diverging throat structure is in alignment with said air orifice member and connected to said conduit structure.

11. The system as claimed in claim 10 wherein the cross-sectional area of said throat is at least 25 percent greater than the cross-sectional area of said air orifice and the cross-sectional area of said inlet port means is at least 25 percent greater than the cross-sectional area of said throat.

12. The system as claimed in claim 11 wherein said tubular wall member is cylindrical in configuration and the length of said tubular wall member is at least three times its diameter.

13. The system as claimed in claim 12 wherein a cooling chamber is formed in said other end wall structure surrounding said outlet port means and said conduit structure is connected to said cooling chamber, and further including an auxiliary conduit and expansion mechanism connected between said cooling chamber and said inlet port means.

14. The system as claimed in claim 13 wherein said restriction structure further includes a check valve disposed in said rigid conduit member. 

1. A burner system comprising a source of pressurized air, a source of pressurized gaseous fuel, a combustion chamber having an uncooled tubular wall member, and end wall structure secured to said tubular wall member at each end thereof, inlet port means in one of said end wall structures, outlet port means in the other end wall structure, the area of said outlet port means being at least 25 percent greater than the area of said inlet port means, conduit structure for supplying a mixture of air and gaseous fuel from said sources for flow through said inlet port means to said combustion chamber at a steady state velocity in the range of 500-1500 feet per second, and restriction structure spaced from said combustion chamber and connected to said conduit structure for restricting the flow of transient pressure waves from said combustion chamber towards said sources and damping acoustical oscillations within said combustion chamber.
 2. The system as claimed in claim 1 wherein a cooling chamber is formed in said other end wall structure surrounding said outlet port means and said conduit structure is connected to said cooling chamber, and further including an auxiliary conduit and expansion mechanism connected between said cooling chamber and said inlet port means.
 3. The system as claimed in claim 2 and further including an annular cooling flange in said cooling chamber.
 4. The system as claimed in claim 1 wherein said restriction structure includes a mixer structure that has an air orifice member disposed in a plenum chamber into which said gaseous fuel is introduced and a converging-diverging throat structure is in alignment with said air orifice member and connected to said conduit structure.
 5. The system as claimed in claim 4 wherein the cross-sectional area of said throat is at least 25 percent greater than the cross-sectional area of said air orifice.
 6. The system as claimed in claim 5 wherein the cross-sectional area of said inlet port means is at least 25% greater than the cross-sectional area of said throat.
 7. The system as claimed in claim 1 wherein the length of said tubular wall member is at least three times its major cross-sectional dimension.
 8. The system as claimed in claim 7 wherein said tubular wall member is cylindrical in configuration.
 9. The system as claimed in claim 1 for use in removing foreign material from structural surfaces wherein said restricting structure includes a mixer unit and said conduit structure includes a rigid conduit member havinG a handle attached thereto for manipulating the combustion chamber and a flexible conduit member extending between said rigid conduit member and said mixer unit.
 10. The system as claimed in claim 9 wherein said mixer unit includes an air orifice member disposed in a plenum chamber into which said gaseous fuel is introduced and a converging-diverging throat structure is in alignment with said air orifice member and connected to said conduit structure.
 11. The system as claimed in claim 10 wherein the cross-sectional area of said throat is at least 25 percent greater than the cross-sectional area of said air orifice and the cross-sectional area of said inlet port means is at least 25 percent greater than the cross-sectional area of said throat.
 12. The system as claimed in claim 11 wherein said tubular wall member is cylindrical in configuration and the length of said tubular wall member is at least three times its diameter.
 13. The system as claimed in claim 12 wherein a cooling chamber is formed in said other end wall structure surrounding said outlet port means and said conduit structure is connected to said cooling chamber, and further including an auxiliary conduit and expansion mechanism connected between said cooling chamber and said inlet port means.
 14. The system as claimed in claim 13 wherein said restriction structure further includes a check valve disposed in said rigid conduit member. 